Segment Information (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Document Period End Date			Sep. 30, 2018
Revenues	$ 2,778	$ 2,752	$ 7,074	$ 6,829
Adjusted EBITDA	476	482	639	595
Non Vehicle Related Depreciation And Amortization	62	66	190	194
Restructuring and other related charges	4	7	14	52
Income before income taxes	355	364	264	210
Assets Under Vehicle Programs	13,602		13,602		$ 11,879
Total assets exclusive of assets under vehicle programs	6,139		6,139		5,820
Americas
Segment Reporting Information [Line Items]
Adjusted EBITDA	313	303	435	379
Assets Under Vehicle Programs	9,900		9,900		9,000
International [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	178	194	252	260
Assets Under Vehicle Programs	3,700		3,700		$ 2,900
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ (15)	$ (15)	$ (48)	$ (44)